Steam distillation of polyphenyl ethers under reduced pressure with or without alumina treatment



May 19, 1970 w, R00 ETAL 3,513,077

STEAM DISTILLATION OF POLYPHENYL ETHERS UNDER REDUCED PRESSURE WITH OR WITHOUT ALUMINA TREATMENT Filed June 21, 1966 VACUUM I SOURCE CONDENSER DI STILLATION COLUMN DISTILLED PRODUCT FEED CONTACTING STEAM CHAMBER INVENTORS CHARLES W. ROOS DARIO R. COVA BYE/w TM ATTORNEY United States Patent US. Cl. 203-29 6 Claims ABSTRACT OF THE DISCLOSURE The corrosiveness and oxidative stability of polyphenyl ethers, polyphenyl thioethers, phenoxy biphenyls and mixtures thereof is greatly improved by subjecting such compounds to a subatmospheric pressure distillation in the presence of steam.

This invention relates to a process for the treatment of functional fluids to improve their oxidative stability and purity. More particularly, this invention relates to a process for the treatment of functional fluids which comprises fractionating such fluids in the presence of steam and under reduced pressure.

Because of the wide variety of applications under which functional fluids, including lubricants and hydraulic fluids, are utilized, a union of many properties, both physical and chemical, are needed to fulfill the demands often made thereon. One of the most rigorous demands on fluids is made by jet aircraft hydraulic systems and jet engine lubrication systems. For example, as the speed and altitude of operation of jet powered aircraft increases, lubrication problems also increase because of higher operating temperatures and higher bearing pressures resulting from the increased thrust needed to obtain higher speeds and altitudes. Thus, the service conditions encountered by functional fluids become increasingly severe, and therefore, the useful life of such fluids is shortened.

The useful life of any lubricant or hydraulic fluid can be adjudged on the basis of many criteria such as the extent of viscosity increase, the extent of corrosion to metal surfaces in contact with the lubricant and the extent of engine deposits. Those skilled in the art have found various ways to improve lubricants and to thus retard or prevent the effects which shorten the useful life of a lubricant. Thus, for example, small amounts of other materials, or additives, can be added to lubricants in order to affect one or more of the properties of the base lubricant. Oftentimes, however, it is difficult, especially as operating temperatures are increased, to find additives which will still perform the function for which they are added and yet not inject other problems. Thus, such functional fluids are preferably stabilized by treatment before their actual use rather than by the incorporation of additives.

Polyphenyl ethers, polyphenyl thioethers and phenoxy biphenyls have been proposed as compounds which can be employed as functional fluids in many different types of applications, such as hydraulic fluids, synthetic lubricants and heat transfer fluids.

It has now been found that the purity and the oxidative stability and thus the useful life of certain aromatic compounds, namely polyphenyl ethers, polyphenyl thioethers and phenoxybiphenyls can be greatly extended and their corrosiveness to metals reduced even under the severe conditions encountered in jet engines and other devices operating at temperatures of the order of 600 F. and higher by contacting such compounds with steam and simultaneously subjecting such compounds to subatmospheric pressure at a temperature sufficient to produce 3,513,07 7 Patented May 19, 1970 fractionation of the compounds. Also, by the process of this invention, significant improvements in the color and odor of such compounds are realized and their corrosiveness toward certain metals is significantly reduced.

It is, therefore, an object of this invention to provide a method of increasing the oxidation resistance of polyphenyl ethers, polyphenyl thioethers and phenoxybiphenyls. Another object of this invention is to provide highly purified polyphenyl ethers, polyphenyl thioethers and phenoxybiphenyls. Another object of this invention is to reduce the corrosivity of polyphenyl ethers, polyphenyl thioethers and phenoxybiphenyls toward certain metals. Other objects will be apparent from the following de scription of this invention.

According to the method of this invention, a material selected from polyphenyl ethers, polyphenyl thioethers, phenoxybiphenyls and mixtures thereof are contacted with steam while being subjected simultaneously to reduced pressure. Broadly, the simultaneous treatment comprises subjecting such material to a sufliciently low pressure, at least under about 500 millimeters of mercury, while maintaining the material at a pot temperature in the range of from about 200 C. up to the thermal decomposition temperature of such material and injecting steam into the material then passing the vapors coming from the liquid through a fractionation device.

The figure is a schematic diagram of the process of this invention. In the figure the feed of polyphenyl ethers, phenoxybiphenyls and mixtures thereof is contacted with steam in the contacting chamber and the vapors passed through the distillation column and condensed in the condenser to yield the distilled product. The process of this invention being conducted under reduced pressure brought about by placing the system under a vacuum from a vacuum source such as a vacuum pump or the like.

As used herein the term fractionation is intended to mean any distillation carried out in such a way that the vapor rising from the liquid comes in contact with a condensed portion of vapor previously evolved from the same source. In the process of this invention, the vapors are brought from the fractionator and condensed. Although the process of this invention can be carried out in other types of equipment which accomplishes the desired fractionation technique of liquid-vapor contact, the invention will be described with particular reference to a multiplate fractionating column.

One class of materials useful in the method of this invention is polyphenyl ethers having from 3 to 7 benzene rings and from 2 to 6 oxygen atoms.

Other materials useful in the method of this invention are those consisting exclusively of benzene rings and include ether oxygen atoms linking said rings exemplified by the phenoxybiphenyls such as biphenylyl phenoxyphenyl ether, biphenylyloxybenzene, bis(biphenylyloxyphenyl) ether, bisphenoxybiphenyl and the like.

A preferred class of the polyphenyl ethers are those consisting of benzene rings joined in a chain by oxygen atoms as ether linkages between each ring, of the formula C H O(C H O) -C H where n is an integer of from 1 to 5. Examples of the polyphenyl ethers contemplated in this class are the bis(phenoxyphenyl) ethers (4 benzene rings joined in a chain by 3 oxygen atoms), illustrative of which is bis(m-phenoxyphenyl) ether and the bis(phenoxyphenoxy) benzenes. Illustrative of the bis(phenoxyphenoxy) benzenes are m-bis( m-phenoxyphenoxy)benzene, m-bis (p-phenoxyphenoxy)benzene, obis(o-phenoxyphenoxy) benzene, and so forth. Further, the polyphenyl ethers contemplated therein include the bis(phenoxyphenoxyphenyl) ethers such as bis[m-(mphenoxyphenoxy)phenyl] ether, bis[p (p phenoxyphenoxy)phenyl] ether, and n1 (m phenoxyphenoxy) phenyl m-(o-phenoxyphenoxy)phenyl ether, and the bis (phenoxyphenoxyphenoxy)benzenes such as m-bis [In-(n1- phenoxyphenoxy)phenoxy] benzene, p bis[p (m-phenoxyphenoxy)phenoxy] benzene and m-bis[m-(phenoxyphenoxy)phenoxy] benzene.

The preferred polyphenyl ethers are those having all their ether linkages in the meta positions since the all meta-linked ethers are particularly advantageous because of their wide liquid range and high thermal stability. However, mixtures of the polyphenyl ethers, either isomeric mixtures or mixtures of homologous ethers, can also advantageously be used in some applications, especially where particular properties such as lower solidification points are required. Mixtures of polyphenyl ethers in which the non-terminal phenylene rings are linked through oxygen atoms in the meta and para positions have been found to be particularly suitable to provide compositions with wide liquid ranges. Of the mixtures having only meta and para linkages, a preferred polyphenyl ether mixture of this invention is the mixture of bis(phenoxyphenoxy)benzenes wherein the non-terminal phenylene rings are linked through oxygen atoms in the meta and para position, and composed by weight of about 65% m-bis(m-phenoxyphenoxy)benzene, 30% m-[(mphenoxyphenoxy) (p-phenoxyphenoxy)] benzene and m-bis(p-phenoxyphenoxy)benzene. Such a mixture solidifies at below room temperature (that is, below about 70 F.) whereas the three components solidify individually at temperatures above normal room temperatures.

Other examples of such preferred polyphenyl ether compositions are those containing, in percent by weight, from about 0% to 6% of o-bis(m-phenoxyphenoxy) benzene 1), about 40% to 85% of m-bis(m-phenoxyphenoxy)benzene (2), about 0% to 40% of m-[(niphenoxyphenoxy) (p-phenoxyphenoxy)] benzene (3), about 0% to 12% of p-bis(m-phenoxyphenoxy) benzene (4), about 0% to of p-[(p-phenoxyphenoxy) (mphenoxyphenoxy)] benzene (5), and about 0% to 6% of m-bis(p-phenoxyphenoxy) benzene, (6).

Typical compositions of such preferred compositions are listed below. The number in parenthesis refers to the compound mentioned above having the same number thereafter.

TYPICAL COMPOSITIONS Compositions, percent by weight of components Component A B C D Another class of material which can be employed in process of this invention is polyphenyl thioethers. As used herein the term polyphenyl thioether means a compound or mixture of compounds represented by the formulae:

where m is a whole number from 0 to 6,

where A and A are each selected from oxygen and sulfur,

where x and y are whole numbers from 0 to 3 and the sum of x+y is from 1 to 6 and A and A are each selected from oxygen and sulfur but at least one of A and A is sulfur, and

(R3) (R4) 1 A I was 1 where R R R and R are each selected from the group consisting of alkyl, alkoxy, haloalkyl, said alkyl and alkoxy groups having from 1 to 4 carbon atoms, hydrogen and halogen, A, A and A are each selected from the group consisting of oxygen and sulfur provided at least one of A, A and A is sulfur, m and n are integers from 0 to 3 provided the sum of m-l-n is at least 1 and mixtures of the foregoing compounds.

Examples of such polyphenyl thioethers are:

2,3-bis (phenylmercapto)diphenyl ether 2,4'-bis(phenylmercapto)diphenyl ether 4,4'-bis (m-tolylmercapto diphenyl ether 3,3'-bis(m-tolylmercapto) diphenyl ether 2,4'-bis(m-tolylmercapto)diphenyl ether 3,4-bis(m-tolylmercapto)diphenyl ether 3,3'bis(p-tolylmercapto)diphenyl ether 3,3'-bis(xylylmercapto)diphenyl ether 4,4-bis xylylmercapto) diphenyl ether 3,4'-bis(xylylmercapto)diphenyl ether 3,4'-bis(m-isopropylphenylmercapto)diphenyl ether 2-m-tolyloxy-2'-phenylmercaptodiphenyl sulfide 2,4'-bis(m-isopropylphenylmercapto)diphenyl ether 3,3'-bis(m-isopropylphenylmercapto diphenyl ether 2,4-bis (m-isopropylphenylmercapto diphenyl ether 3 ,4'-bis p-tert-butylphenylmercapto diphenyl ether 4,4-bis(p-tert-butylphenylmercapto) diphenyl ether 3,3- bis(p-tert-butylphenylmercapto)diphenyl ether 3 ,3 -bis (m-chlorophenylmercapto diphenyl ether 3,3-bis(m-ditert-butylphenylmercapto)diphenyl ether 3,3 -bis (m-chlorophenylmercapto diphenyl ether 4,4-bis (m-chlorophenylmercapto diphenyl ether 3 3'-bis (m-trifluoromethylphenylmercapto diphenyl ether 4,4-bis (m-trifluoromethylphenylmercapto) diphenyl ether 3,4-bis(m-trifiuoromethylphenylmercapto) diphenyl ether 2,3-bis(m-trifluoromethylphenylmercapto) diphenyl ether 3,3bis(p-trifluoromethylphenylmercapto)diphenyl ether 3,3 '-bis o-trifiuoromethylphenylmercapto diphenyl ether 3, 3 '-bis (m-methoxyphenylmercapto) diphenyl ether 3,4-bis(m-isopropoxyphenylmercapto)diphenyl ether 3,4-bis(m-perfluorobutylphenylmercapto)diphenyl ether 2-p-tolyloxy-3'-pheny1mercaptodiphenyl sulfide 2-o-tolyloxy-4'-phenylmercaptodiphenyl sulfide 3-m-tolyloxy-3'-phenylmercaptodiphenyl sulfide 3-rn-tolyloxy-4'-phenylmercaptodiphenyl sulfide 4-m-toly1oxy-4'-phenylmercaptodiphenyl sulfide 3-xylyloxy-4-phenylmercaptodiphenyl sulfide 3-xylyloxy-3'-phenylmercaptodiphenyl sulfide 3-phenoxy-3-m-tolylmercaptodiphenyl sulfide 3-phenoxy-4'-m-tolylmercaptodiphenyl sulfide Z-phenoxy-3'-p-tolylmercaptodiphenyl sulfide 3-phenoxy-4"m-isopropylphenylmercaptodiphenyl sulfide 3-phenoxy-3-misopropylphenylmercaptodiphenyl sulfide 3-m-tolyloxy-3'-m-isopropylphenylmercaptodiphenyl sulfide 4-m-trifluoromethylphenoxy-4'-phenylmercaptodiphenyl sulfide 3-m-trifluoromethylphenoxy-4'-phenylmercaptodiphenyl sulfide 2In-trifluoromethylphenoxy-4'-phenylmercaptodiphenyl sulfide 40 3-m-trifluoromethylphenoxy-3-phenylmercaptodiphenyl sulfide 3-p-chlorophenoxy-3'-phenylrnercaptodiphenyl sulfide, and 3-m-bromophenoxy-4'-phenylmercaptodiphenyl sulfide.

In carrying out the process of this invention the material to be treated is heated to a suitable temperature such that under subatmospheric pressure vaporization takes place. For most material this temperature is from about 200 C. to about 350 0., depending on the particular 0 material employed. At those temperatures efiicient vaporization takes place at pressures from about 50 to 100 millimeters of mercury. Lower pressures can be employed depending on capability of the equipment used.

The injection of steam can be accomplished by any means which provides substantial contact between the liquid material and the steam, although the material can be contacted above the surface in the still pot. A subsurface sparger in the still pot has been found to provide desirable results. It is advantageous to use dry steam although not critical to the process.

The amount of steam employed is directly proportional to the amount of material to be vaporized under the conditions of temperature and pressure employed in the fractionation device. Thus, for example, to treat 100 pounds of bis(phenoxyphenoxy)benzene according to the method of this invention at a temperature of about 325 C. and an absolute pressure of about 75 mm. of mercury there would be required about 52 pounds of steam. When a portion of the condensed material is returned to the fractionation device and is revaporized additional steam is necessary. The rate of flow of the steam is dependent upon the capacity of the equipment employed.

The vapors leaving the fractionating column are condensed by any conventional means. When highly pure products are desired (995+ percent) the condenser is equipped with means to return a portion of the product to the still. The reflux ratio of condensed vapor returned to the still to that sent to a recovery vessel is desirably from about 1 to 2 to about 5 to 1.

The following non-limiting examples illustrate the process of this invention.

Example 1 About 1600 grams of crude bis(phenoxyphenoxy)benzene containing 2, 3, 4 and 6 ring polyphenyl ethers and high boiling tars were treated in a 15 plate, 2-inch diameter Oldershaw column under absolute pressure of about millimeters of mercury and a temperature of about 275 C. Steam was admitted into the body of the fluid at a rate of 560 grams per hour. The fluid was fractionated by the stepwise increase of pot temperature to a maximum of 342 C. over a period of 12 hours. The main cut was taken at pot temperatures of from 320 C. to 342 C., with a reflux ratio of 1 to 1. The product obtained in the main cut analyzed 99.6% bis(phenoxyphenoxy)benzene.

Example 2 The residue remaining in the still pot of the Oldershaw column in Example 1, which contained from 30 to 40% by weight, 6-ring poylphenyl ether and higher boiling material was fractionated under absolute pressure of 59 millimeters of mercury and pot temperatures in the range of from 350 C. to 369 C., While collecting the main cut at a reflux ratio of 2:1. Steam was injected into the liquid at a rate of 530 grams per hour for 7 hours. The main cut analyzed 92.7% bis(phenoxyphenoxyphenyl) ether.

Example 3 About 1300 grams of crude bis(phenylmercapto) benzene were placed in a 2-inch diameter, 15 plate Oldershaw column and heated to a pot temperature of about 220 C. under an absolute pressure of 60 mm. of mercury. Dry steam was sparged into the fluid at 630 grams per hour. The fluid was fractionated at pot temperatures in the range of 246 to 249 C. After taking a 41 gram forecut, four additional cuts were taken at a reflux ratio of 4 to 1 and 3 cuts taken at a reflux ratio of 1 to 1, totaling 1061 grams of products. The last three cuts were analyzed by g.l.c. and found to be bis(phenylmercapto)benzene. The cuts were combined to form a fluid having an average purity of 99.7% by weight, a sample of which was taken for comparison with a sample of equal purity obtained by vacuum distillation.

The useful life of a functional fluid can be adjudged on the basis of many criteria such as the extent of viscosity increase under the conditions of use. The major bench scale method used for evaluating the oxidative stability of a functional fluid is the procedure given in Federal Test Specification 791, Method 5308 according to which the lubricant to be tested is heated at a specified temperature in the presence of certain metals and oxygen and the viscosity increase of the lubricant is determined.

Compositions were tested according to the procedure of Federal Test Specification 791, Method 5308 except that the temperature was held at 600 F. instead of 500 F. and the metal specimens used were, as specified in said procedure, steel, copper, silver, titanium, magnesium alloy and aluminum alloy. Additionally, information as to the corrosiveness of the compositions to metals was obtained. However, only the results upon copper and silver are repeated since the untreated compositions tested had essentially no effect on the other metals employed. Viscosity measurements were made according to ASTM Method D44553T using a Cannon-Fenske modified Ostwald viscosimeter. The percentage of viscosity increase was determined by taking the difference in viscosity of a composition before and after it was heated, dividing the diflerence by the original viscosity and multiplying the quotient by 100. Samples of the main cut of Example 1 and of the blended composition of Example 3 and samples of materials obtained by conventional vacuum distillation were tested as described above. The corrosiveness to metals was determined by weighing metal specimens of known size before and after the test. The results of the test appear in Table I below as percent viscosity increase at 100 F.

TABLE I Percent Metal Attack, Viscosity mg./cm. Increase at Test Fluid 100 F. Cu Ag Vacuum distilled bis(phenoxyphenoxy)benzene 18 Product of example 1 9. 6 Vacuum distilled bis(phenylmercapto)benzene 8 5. 74 1. 92 Product of example 3 3. 3 2. 90 1. 19

A portion of bis(phenylmercapto)benzene obtained from vacuum distillation and a portion of the blended product of Example 3 were treated with activated alumina as follows. A four-inch by eighteen-inch glass column, containing, from the bottom, a one-quarter inch layer of filter aid and a ten-inch layer of activated alumina, was fitted to a receiving vessel capable of sustaining subatmospheric pressure. Each portion of fluid at about 50 to 60 C. was passed through the column while maintaining a vacuum in the receiving vessel. After such treatment the samples were subjected to oxidation and corrosion tests as explained above. The results of such tests appear in Table II below. While it is preferred to perform the treatments in the order shown in the above example, alternatively the two treatments may be performed in reverse order, i.e., contact the fluid first with alumina and thereafter treat the fluid by vacuum steam fractionation.

From the above it is clearly evident that the treatment of materials according to the process of this invention provides compositions having a greatly increased oxidative stability and reduced corrosivity toward metals and therefore a greatly extended useful life. In regard to the extention of useful life, it has been found that the test procedure described above correlates quite Well with the results obtained under full scale aircraft gas turbine hearing tests and under conditions of actual use. It has been found that the magnitude of change in the viscosity at 100 F. as measured by the test procedure is representative of the extent of increased service life obtainable under actual conditions. Thus, for example, the decrease in viscosity increase at 100 F. obtained by treatment of materials according to this invention was on the order of about 2 times (i.e., the viscosity increase at F. for the materials which were vacuum distilled according to the prior art as compared to the viscosity increase for the treated materials according to this invention was about 2 times as great). Based on these results in the bench test, it would be expected that a servicelife increase of about 2 times that obtained from the materials used can be obtained by treating the fluid according to the method of this invention. Similar correlations are obtained with other material contemplated. It should also be noted that polyphenyl thioethers treated according to the process of this invention have improved odor and color characteristics in addition to an extended useful life as indicated by improved stability and decreased corrosivity toward metal.

While this invention has been described with respect to specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.

The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process comprising contacting a material selected from the group consisting of polyphenyl ethers, phenoxybiphenyl, and mixtures thereof with steam while simultaneously subjecting said material to subatmospheric pressure at a temperature sufficient to produce distillation of said material and recovering said material in a more purified form as a distillate.

2. A process as in claim 1 wherein the distillate is contacted with alumina and thereafter separating said distillate from said alumina.

3. A process of claim 1 where the material contains bis(phenoxyphenoxy)benzene.

4. A process of claim 1 where the subatmospheric pressure is below about 200 millimeters of mercury and the temperature is above about 200 C.

5. A process of claim 1 where the material contains bis(phenoxyphenoxyphenyl) lether.

6. A process comprising contacting a material selected from the group consisting of polyphenyl ethers, phenoxybiphenyls, and mixtures thereof with alumina and separating said material from said alumina, said contacting being prior to contacting said material with steam while simultaneously subjecting said material to subatmospheric pressure sufficient to produce distillation of said material and recovering said material as a distillate in a more purified form.

References Cited UNITED STATES PATENTS 2,060,716 11/1936 Arvin 260-613 3,056,842 10/1962 'Vi lars 260-613 3,083,234 3/1963 Sax 260613 3,159,684 12/1964 Merica 260-613 3,240,817 3/1966 Carlson 260613 3,362,934 1/1968 Balon 260613 3,363,005 l/l968 Alvarez 260613 3,409,677 11/1968 Duncker et al. 2606l3 WILBUR L. BASCOMB IR., Primary Examiner US. Cl. X.R. 

